This invention relates to extra high voltage circuit breakers and more specifically relates to a novel closing resistor module which can be easily installed within the interior of the housing of an extra high voltage circuit breaker.
Extra high voltage circuit breakers are well known and may be rated at voltages such as 362 kilovolts or 550 kilovolts. A common construction for an extra high voltage circuit breaker employs an outer housing which may be grounded (a dead tank) which has insulator bushings entering the tank at two spaced locations along its length. One or more modular interrupter assemblies supported in series are then connected between the interior portions of the insulating bushings.
It is common in such extra high voltage circuit breakers to employ a closing resistor since switching surges may be more severe than lightning overvoltages. Prior art closing resistors consist of a stack of resistor disks or other elements in parallel with each of the interrupter breaks. The resistor contacts close before the interrupter contacts to pre-insert the resistor in the circuit. The main contacts close later to short circuit the closing resistor. The resistor contact is thereafter opened to remove the resistor from the circuit prior to reopening the interrupter contacts. The closing resistor reduces switching surge overvoltages on the line which otherwise might exceed the lightning basic insulation rating of the device.
Closing resistors are commonly located physically adjacent and coextensive with the interrupter assembly or are located elsewhere within the circuit breaker housing. Closing resistors are frequently quite long, for example, two meters long for a 550 kv circuit breaker. Thus closing resistors and their contacts are not easily mounted within the breaker housing. Moreover, it is not easy to treat the resistor as an add-on option in the design and production of the breaker.
Another problem with closing resistor assemblies in the prior art is that relatively complex operating mechanisms have been needed to cause the closing resistor contacts to close just prior to the interrupter contacts and with high speed and to open before the interrupter contacts open. Thus, complex linkages have been required in the operating mechanisms of the closing resistors. This has further complicated the main operating mechanism of the circuit breaker.